A rotate mechanism is a device that is utilized to quickly rotate a large mass, such as, for example, a mold component of an injection molding system, between two or more angular positions. In injection molding applications, it is advantageous to employ a rotating mold to accommodate multi-shot molding operations. For example, consider a two-shot injection molding process using a mold having cavities defining two parts to be molded. The mold rotates to allow each cavity to be exposed to two different molding operations, each operation providing one of the two shots of injection molding.
In such a device, the rotate mechanism is desirably adapted to accelerate the mold component quickly and then decelerate the component to a complete stop at the desired location without damaging the equipment and/or the mold component. In addition to mold components, other machine tool elements often have similar rotation requirements for use in carrying out other multistep work processes.
A number of rotate mechanisms have heretofore been designed; however, each of such designs has a number of drawbacks associated therewith. For example, rotate mechanisms have heretofore been designed in which the large mass is moved by use of an assembly including a rotary motor and a number of belts or chains which are entrained through a system of pulleys, gears, and/or sprockets. However, such rotate mechanisms are relatively mechanically complex thereby increasing costs associated with manufacture and maintenance of the mechanism.
Moreover, rotate mechanisms have also been designed in which the large mass is moved by use of a rack and pinion gear drive which is driven by air or hydraulic cylinders. However, it has been found that rotate mechanisms designed in such a manner are limited as to the amount of weight that they can adequately rotate and are generally less durable relative to other designs. Rotate mechanisms have also been designed to include an arrangement of electric servo motors and associated gear drives. While such designs have a number of desirable performance characteristics (e.g. relatively fast rotational velocities, high accelerations, and precise positioning), such designs are relatively expensive and, as a result, are seldom used.
Another heretofore designed rotate mechanism is shown in U.S. Pat. No. 5,837,301 issued to Arnott et al. Rotational movement is created by alternately moving a turret block in a linear direction toward and away from a fixed platen using of a cylinder assembly. In particular, as the turret block is moved away from the fixed platen, a sliding plate secured to an end of a linkage rod slides in a track defined in the fixed platen. When the sliding plate reaches the end of the track, the rod pulls the rotating turret thereby causing the rotating turret to rotate. When the turret block is at its furthest distance away from the fixed platen, the turret block has rotated through ninety degrees (90°) of travel. As the turret block is subsequently moved back toward the fixed platen, the rod pushes the turret block thereby causing the turret block to continue rotating in the same direction through the remaining ninety degrees (90°) of travel. As the turret block is moved away from the fixed platen during the next cycle of the mechanism, the process described above is repeated with the turret block being rotating in the opposite direction.
As described, the device disclosed in the Arnott reference relies on linear movement/displacement of the rotary platen (i.e. the turret block) in order to create the forces necessary to rotate the turret block. Hence, a relatively large operating area is required to accommodate for the linear motion of the turret block. Additionally, the device disclosed in the Arnott reference requires separate mechanisms (i.e. the cylinder assembly and the linkage rod) for providing the motive force to rotate the turret block and controlling the direction of rotation of the turret block thereby increasing the mechanical complexity of the device.
Another problem particularly related to injection molding and certain other types of processes arises from the large forces associated with the molding process. Injection molding presses can generate forces of 100 tons or more. When a rotate mechanism is used in such a device, the rotate mechanism may be subject to a greater part of that force. In particular, the rotate mechanism is subject to such force in the axial direction with respect to its direction of rotation. To withstand such axial force, it is desirable to maximize surface contact between the rotating element and the stationary element. The problem arises from the fact that such maximization of surface area undesirably inhibits rotation.
What is needed therefore is a rotate mechanism that overcomes one or more of the above-described drawbacks. What is particularly needed is a relatively cost effective, compact rotate mechanism that is capable of rotating relatively large masses very rapidly between stop locations. Such a rotate mechanism would desirably be capable of stopping at relatively precise locations, while also providing high rotational velocities and accelerations. Moreover, it is further desirable for such a rotate mechanism to be able to withstand large axial forces, such as those associated with a mold press.